1. Field of the Invention
The invention relates to an endless power transmission belt.
2. Description of the Prior Art
In multiple constructions endless power transmission belts are known having a cabled reinforcement embedded in a rubbery material matrix which are adapted for cooperating with the pulleys of a driven shaft, and of a drive shaft respectively. Thus there exist, besides V belts, with or without teeth, ribbed belts--that is to say, belts whose section through a diametrical plane, is a profile with an internal face formed with adjacent teeth, having a triangular or trapezoidal cross section. Such a belt is provided for cooperating with pulleys whose rim has a mating profile--that is to say, has adjacent grooves with triangular or trapezoidal cross section. Such belts, which find application in very numerous fields, are designated in schedules by the letters H, J, A, L or M, which define the pitch and/or the shape of the teeth as well as the radial thickness of the belts. Those of type H or J, with tooth pitches of 1.6 and 2.34 mm and thickness of about 3 mm and 4 mm,respectively, are used in the electric household appliance field, particularly for driving clothes washing or clothes drying machine drums from the electric motors of these machines. In such applications, the rotational speeds are of the order of 400 to 1200 rpm. Tensioning of the belt, after it has been fitted over the pulley of the drive shaft and over the pulley of the driven shaft, is generally carried out by moving the motor mounted on a pivoting shoe and locking it in position when the required tension is reached or by means of a spring tensioner when the powers to be transmitted are lower than in the preceding case.
Whatever the operating mode used, the tension must be adjusted accurately so that the rotational speed of the driven member is very close to the desired theoretical value, relatively small variations with respect to this theoretical value causing unsatisfactory operation for washing and drying clothes, for example. The result is that to the cost of the pivoting means for adjusting the between axis distance of the driven and drive shafts is added that of the adjustment of the tension after fitting the belt on the pulleys with which it cooperates. Furthermore, neither the mounting of the motor (whose position must be adjusted) nor that of the belt can be carried out automatically.
To overcome these difficulties, attempts were then made to provide endless power transmission belts that were sufficiently extendable so that they could be mounted on the pulleys with which they cooperate without modifying the distance therebetween, on the one hand, and, on the other, that were sufficiently resilient so that, after mounting, they themselves provided the required tension for good power transmission. Such belts, manufactured by extruding or molding a thermoplastic or thermosetting material, particularly with a polyester type resing basis, have, however, proved unsatisfactory, mainly because of the low adhesion between them and the members with which they cooperate.